linux-kernel - Re: [PATCH] arm64: dts: imx8mm-kontron-n801x-som: do not allow to switch off buck2

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Date:   Fri, 17 Sep 2021 09:28:51 +0200
From:   Heiko Thiery <heiko.thiery@...il.com>
To:     Frieder Schrempf <frieder.schrempf@...tron.de>
Cc:     Michael Walle <michael@...le.cc>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Shengjiu Wang <shengjiu.wang@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Guido Günther <agx@...xcpu.org>,
        "Angus Ainslie (Purism)" <angus@...ea.ca>
Subject: Re: [PATCH] arm64: dts: imx8mm-kontron-n801x-som: do not allow to
 switch off buck2

Hi Frieder,

Am Mi., 15. Sept. 2021 um 14:09 Uhr schrieb Frieder Schrempf
<frieder.schrempf@...tron.de>:
>
> On 15.09.21 14:05, Michael Walle wrote:
> > Am 2021-09-15 14:03, schrieb Heiko Thiery:
> >> The buck2 output of the PMIC is the VDD core voltage of the cpu.
> >> Switching off this will poweroff the CPU. Add the 'regulator-always-on'
> >> property to avoid this.
> >
> > Mh, have this ever worked? Is there a commit which introduced a regression?
>
> Yes, this did work before, even without 'regulator-always-on'. I
> currently don't understand why this is needed. The regulator is
> referenced in the CPU nodes as 'cpu-supply'. This should be enough to
> not disable it as long as the CPU is up.

I rechecked that with 5.11, 5.10 and 5.9 and I see on all of them the
same issue:

[ 31.716031] vdd-5v: disabling
[ 31.719032] rst-usb-eth2: disabling
[ 31.722553] buck2: disabling

While on that I tried to compare with other boards and see that they
also have the cpu-voltage marked as "regulator-always-on". The only
exception in dts/freescale is in imx8mq-librem5-devkit.dts [1] that
has not set this property.

I agree with you and don't understand why this is happening. Has
anyone else an explanation?

[1] https://elixir.bootlin.com/linux/latest/source/arch/arm64/boot/dts/freescale/imx8mq-librem5-devkit.dts#L319

-- 
Heiko